1. Field of the Invention
The present invention relates generally to cochlear implant systems and, more particularly, to using a genetic algorithm to fit a cochlear implant system to a patient.
2. Related Art
Many medical devices have structural and/or functional features which are to be adjusted for an individual patient. The process by which a medical device is tailored or customized for the specific needs of a patient is commonly referred to as fitting. One type of medical device which is typically fitted to individual recipients is a cochlear™ implant system.
Cochlear™ implant systems provide the benefit of hearing to individuals suffering from severe to profound hearing loss. Hearing loss in such individuals is often due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Cochlear™ implant systems essentially simulate the auditory nerves by directly delivering electrical stimulation to the auditory nerve fibers. This causes the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered by the auditory nerve. Examples of cochlear implant systems are described, by way of example, in U.S. Pat. Nos. 4,532,930, 6,537,200, 6,565,503, 6,575,894, and 6,697,674, among others.
Conventional cochlear™ implant systems commonly include an external assembly directly or indirectly attached to the body of the patient (sometimes referred to herein as the recipient), and an internal assembly which is implanted in the patient. The external assembly typically comprises one or more microphones for detecting sound, a speech processing unit that converts detected sound into an electrical coded signal, a power source, and an external transcutaneous transfer coil. The internal assembly typically comprises an internal transcutaneous transfer coil, a stimulator unit located within a recess of the temporal bone of the recipient, and an electrode array positioned in the recipient's cochlea. Completely implantable cochlear implant systems having functionally similar components are under development.
In addition to providing electrical stimulation, some cochlear™ implant systems also include a mechanical stimulation mode of operation. Such so called mixed-mode systems offer rehabilitation by mechanically stimulating a portion of a patient's auditory pathway, either acoustically or physically. For example, there have been approaches to offer rehabilitation with conventional hearing aids via the application of an amplified acoustic signal to the external auditory canal, or by physically stimulating an ossicle of the middle ear or the inner ear via mechanical or hydromechanical stimulation.
Modern cochlear implant systems provide a wide variety of fitting options that can be customized for an individual patient. Because patients are heterogeneous, each patient requires a different set of parameters to maximize speech reception and patient satisfaction. The task of the clinical professional, usually an audiologist, is to select a set of parameters, commonly referred to as a parameter map or, more simply, a MAP, that will provide the best possible speech reception for an individual patient. Because there may be hundreds or thousands of possible parameter maps, it is impractical to experience all of the alternatives and to evaluate the performance of each alternative for an individual patient. Nor is it possible to identify an optimal parameter map by prescription based on a limited set of measurements as is, for example, the case in fitting eyeglasses. Because parameters of cochlear implant systems often interact non-linearly and non-monotonically, it is also not possible to sequentially optimize parameters one at a time, adjusting each in succession to its optimal value.
As a result, clinicians have adopted a variety of approaches for fitting the cochlear implant systems to a patient. Some simply set the parameters to default valves regardless of the individual patients. Others adopt preferred parameter maps, which they believe are good, if not best, for many or most patients. These may be based on personal experience, published performance data, or intuition. Some clinicians evaluate a limited set of alternatives adjusting individual parameters based upon measured perceptual limitations and inferred relationships among the parameters. These approaches are time consuming, costly, and unreliable, and typically fail to achieve the optimal outcome for individual patients.